GPencil: Fill tool refactor and Multiframe in Draw mode

This commit is a refactor of the fill tool to solve several problems we had since the first version of the tool.

Changes:

* The filling speed has been improved for each step of the process with the optimization of each algorithm/function.
* New `AutoFit` option to fill areas outside of the viewport. When enable, the total size of the frame is calculated to fit the filling area.
* New support multiframe filling. Now it is possible to fill multiple similar frames in one go.
* New `Stroke Extension` option to create temporary closing strokes. These strokes can be displayed and adjusted dynamically using wheel mouse or PageUp/Down keys.
* Parameter `Resolution` now is named `Precision` and has been moved to topbar.
* `Resolution` now has decimals and can be lower than 1 to allow quick filling in storyboarding workflows. Maximum value has been set as 5.
* Parameter `Simplify` has been moved to Advanced panel.
* Improved fill outline detection. In some cases, the outline penetrated the area to be filled with unexpected results.
* Fixes some corner case bugs with infinite loops.

As a result of this refactor, also these new functionalities has been added.

* New support for multiframe in `Draw` mode. Any drawing in active frame is duplicated to all selected frame.
* New multiframe display mode. Keyframes before or after of the active frame are displayed using onion colors. This can be disable using Onion overlay options.

5 files changed, 81 insertions, 1 deletions

diff --git a/source/blender/blenkernel/BKE_gpencil.h b/source/blender/blenkernel/BKE_gpencil.h
index b7fad9c891a..a8caf317467 100644
--- a/source/blender/blenkernel/BKE_gpencil.h
+++ b/source/blender/blenkernel/BKE_gpencil.h
@@ -115,6 +115,8 @@ struct bGPDlayer *BKE_gpencil_layer_duplicate(const struct bGPDlayer *gpl_src,
                                               const bool dup_frames,
                                               const bool dup_strokes);
 void BKE_gpencil_frame_copy_strokes(struct bGPDframe *gpf_src, struct bGPDframe *gpf_dst);
+void BKE_gpencil_frame_selected_hash(struct bGPdata *gpd, struct GHash *r_list);
+
 struct bGPDcurve *BKE_gpencil_stroke_curve_duplicate(struct bGPDcurve *gpc_src);
 struct bGPDstroke *BKE_gpencil_stroke_duplicate(struct bGPDstroke *gps_src,
                                                 const bool dup_points,
diff --git a/source/blender/blenkernel/BKE_gpencil_geom.h b/source/blender/blenkernel/BKE_gpencil_geom.h
index 1c86df73d3c..89a794f2df3 100644
--- a/source/blender/blenkernel/BKE_gpencil_geom.h
+++ b/source/blender/blenkernel/BKE_gpencil_geom.h
@@ -149,6 +149,11 @@ void BKE_gpencil_stroke_join(struct bGPDstroke *gps_a,
                              struct bGPDstroke *gps_b,
                              const bool leave_gaps,
                              const bool fit_thickness);
+void BKE_gpencil_stroke_copy_to_keyframes(struct bGPdata *gpd,
+                                          struct bGPDlayer *gpl,
+                                          struct bGPDframe *gpf,
+                                          struct bGPDstroke *gps,
+                                          const bool tail);
 
 bool BKE_gpencil_convert_mesh(struct Main *bmain,
                               struct Depsgraph *depsgraph,
diff --git a/source/blender/blenkernel/intern/brush.c b/source/blender/blenkernel/intern/brush.c
index 1ba5571a26b..59ff59b82e0 100644
--- a/source/blender/blenkernel/intern/brush.c
+++ b/source/blender/blenkernel/intern/brush.c
@@ -975,7 +975,7 @@ void BKE_gpencil_brush_preset_set(Main *bmain, Brush *brush, const short type)
       break;
     }
     case GP_BRUSH_PRESET_FILL_AREA: {
-      brush->size = 20.0f;
+      brush->size = 5.0f;
 
       brush->gpencil_settings->fill_leak = 3;
       brush->gpencil_settings->fill_threshold = 0.1f;
@@ -989,6 +989,8 @@ void BKE_gpencil_brush_preset_set(Main *bmain, Brush *brush, const short type)
       brush->gpencil_settings->draw_smoothlvl = 1;
       brush->gpencil_settings->draw_subdivide = 1;
 
+      brush->gpencil_settings->flag |= GP_BRUSH_FILL_SHOW_EXTENDLINES;
+
       brush->gpencil_settings->icon_id = GP_BRUSH_ICON_FILL;
       brush->gpencil_tool = GPAINT_TOOL_FILL;
       brush->gpencil_settings->vertex_mode = GPPAINT_MODE_FILL;
diff --git a/source/blender/blenkernel/intern/gpencil.c b/source/blender/blenkernel/intern/gpencil.c
index 0c813c170ad..3d0152a6c7d 100644
--- a/source/blender/blenkernel/intern/gpencil.c
+++ b/source/blender/blenkernel/intern/gpencil.c
@@ -851,6 +851,7 @@ bGPDstroke *BKE_gpencil_stroke_new(int mat_idx, int totpoints, short thickness)
 
   gps->mat_nr = mat_idx;
 
+  gps->dvert = NULL;
   gps->editcurve = NULL;
 
   return gps;
@@ -2606,6 +2607,15 @@ void BKE_gpencil_visible_stroke_iter(ViewLayer *view_layer,
       LISTBASE_FOREACH (bGPDframe *, gpf, &gpl->frames) {
         if (gpf == act_gpf || (gpf->flag & GP_FRAME_SELECT)) {
           gpf->runtime.onion_id = 0;
+          if (do_onion) {
+            if (gpf->framenum < act_gpf->framenum) {
+              gpf->runtime.onion_id = -1;
+            }
+            else {
+              gpf->runtime.onion_id = 1;
+            }
+          }
+
           if (sta_gpf == NULL) {
             sta_gpf = gpf;
           }
@@ -2939,4 +2949,26 @@ int BKE_gpencil_material_find_index_by_name_prefix(Object *ob, const char *name_
   return -1;
 }
 
+/* Create a hash with the list of selected frame number. */
+void BKE_gpencil_frame_selected_hash(bGPdata *gpd, struct GHash *r_list)
+{
+  const bool is_multiedit = (bool)GPENCIL_MULTIEDIT_SESSIONS_ON(gpd);
+  bGPDlayer *gpl = BKE_gpencil_layer_active_get(gpd);
+
+  LISTBASE_FOREACH (bGPDlayer *, gpl_iter, &gpd->layers) {
+    if ((gpl != NULL) && (!is_multiedit) && (gpl != gpl_iter)) {
+      continue;
+    }
+
+    LISTBASE_FOREACH (bGPDframe *, gpf, &gpl_iter->frames) {
+      if (((gpf == gpl->actframe) && (!is_multiedit)) ||
+          ((gpf->flag & GP_FRAME_SELECT) && (is_multiedit))) {
+        if (!BLI_ghash_lookup(r_list, POINTER_FROM_INT(gpf->framenum))) {
+          BLI_ghash_insert(r_list, POINTER_FROM_INT(gpf->framenum), gpf);
+        }
+      }
+    }
+  }
+}
+
 /** \} */
diff --git a/source/blender/blenkernel/intern/gpencil_geom.c b/source/blender/blenkernel/intern/gpencil_geom.c
index 60ffa3c3e73..2ef85439a46 100644
--- a/source/blender/blenkernel/intern/gpencil_geom.c
+++ b/source/blender/blenkernel/intern/gpencil_geom.c
@@ -3228,6 +3228,45 @@ void BKE_gpencil_stroke_join(bGPDstroke *gps_a,
   }
 }
 
+/* Copy the stroke of the frame to all frames selected (except current). */
+void BKE_gpencil_stroke_copy_to_keyframes(
+    bGPdata *gpd, bGPDlayer *gpl, bGPDframe *gpf, bGPDstroke *gps, const bool tail)
+{
+  GHash *frame_list = BLI_ghash_int_new_ex(__func__, 64);
+  BKE_gpencil_frame_selected_hash(gpd, frame_list);
+
+  GHashIterator gh_iter;
+  GHASH_ITER (gh_iter, frame_list) {
+    int cfra = POINTER_AS_INT(BLI_ghashIterator_getKey(&gh_iter));
+
+    if (gpf->framenum != cfra) {
+      bGPDframe *gpf_new = BKE_gpencil_layer_frame_find(gpl, cfra);
+      if (gpf_new == NULL) {
+        gpf_new = BKE_gpencil_frame_addnew(gpl, cfra);
+      }
+
+      if (gpf_new == NULL) {
+        continue;
+      }
+
+      bGPDstroke *gps_new = BKE_gpencil_stroke_duplicate(gps, true, true);
+      if (gps_new == NULL) {
+        continue;
+      }
+
+      if (tail) {
+        BLI_addhead(&gpf_new->strokes, gps_new);
+      }
+      else {
+        BLI_addtail(&gpf_new->strokes, gps_new);
+      }
+    }
+  }
+
+  /* Free hash table. */
+  BLI_ghash_free(frame_list, NULL, NULL);
+}
+
 /* Stroke Uniform Subdivide  ------------------------------------- */
 
 typedef struct tSamplePoint {